A conventional UV detection apparatus includes a photovoltaic type sensor device which detects UV light irradiating a light receiving area in response to a change in the flow amount of a photo-induced current. To this end, Si semiconductors having a detection sensitivity to visible light with a wavelength range from 400 nm to 750 nm have been considered in the related art because it reduces cost and can be easily doped. According to the light detection principle of a photovoltaic type sensor device, light having energy of a band gap or greater is irradiated upon a semiconductor of the light receiving area to generate electron/hole pairs, thus separating electrons and holes by a depletion layer, and supplying a current to an external circuit.
A photodiode is known as a photovoltaic type sensor device. Also, as mentioned above, photovoltaic type sensor devices are generally made of Si. Another type of photodiode is a Schottky junction type, in which Si directly contacts a metal electrode. The Schottky junction type is characterized in that the forward voltage drop is low and the switching speed is high. However, the Schottky junction type has a problem in that it produces a large reverse leakage current. For this reason, a metal insulator semiconductor (MIS) Schottky diode using Si has been proposed. This type of device employs a MIS Schottky diode having an Au/SiO2/Si structure.
Meanwhile, Si has sensitivity in a wavelength region of 1 μm or smaller, so it is difficult to extract only UV light in measuring the quantity of light. Therefore, in order to cut light other than UV light, a particular visible light/infrared light cut-off filter is required to be inserted.
Thus, an AlGaN semiconductor or ZnO semiconductor is considered as a semiconductor which is able to selectively absorb and detect only UV light, without using any filter.
Compared to the above devices, a photodiode including Si and a filter has high reliability but has a disadvantage in that it may deteriorate from strong UV irradiation. Further, although an AlGaN semiconductor may not deteriorate from UV irradiation, electron concentration therein is relatively high. Thus, when an AlGaN semiconductor is mass-produced, it may be difficult to take control of the dark current. Meanwhile, when employing a ZnO semiconductor, it has an advantage in that it may not deteriorate from UV irradiation. In addition, since the electron concentration is low, the dark current is stably suppressed.
Thus, for example, a MIS Schottky diode using a ZnO semiconductor is proposed. In this device, an MIS Schottky diode having an Au/Cr/SiO2/ZnO structure is considered.
However, even for a MIS Schottky diode using ZnO, leakage current is not sufficiently restrained during reverse biasing. Further, there is room for improvement of electrical characteristics such as rectifying during forward biasing.